Semiconductor contact structure having wide lower portion embedded in conductive material

Abstract

The present invention provides a semiconductor contact structure and a method of forming the same. An interlayer dielectric is patterned to form a contact hole that exposes a predetermined region of conductive material on a semiconductor substrate. A recess is formed in the conductive material exposed by the contact hole and undercuts the walls that define the sides of the contact hole such that the recess is wider than the contact hole. A contact plug fills the recess as well as the contact hole. The contact plug is maintained in position stably atop the underlying conductive material because the lower part of the contact plug is wider than the upper part of the contact plug. Accordingly, the contact plug will not fall over even if the interlayer dielectric reflows during a subsequent process.

What is claimed is:  
     
       1. A semiconductor contact structure comprising: 
       a semiconductor substrate;  
       an interlayer dielectric layer disposed on said semiconductor substrate, said interlayer dielectric having a contact hole extending therethrough and exposing a region of conductive material on the semiconductor substrate, and said conductive material having an upper surface, and a recess therein contiguous to said contact hole, said recess being located below the upper surface of the conductive material and being wider than said contact hole as taken laterally in a direction extending along the upper surface of said substrate such that said recess undercuts sidewalls that define said contact hole;  
       a spacer lining the sidewalls that define said contact hole, said spacer having a lower portion that extends beneath the level of the upper surface of said conductive material; and  
       a contact plug having a lower portion that rests directly on said conductive material and fills said recess, and an upper portion that fills said contact hole, whereby the lower portion of the contact plug is wider than the upper portion of thereof so that the contact plug is stably supported in the structure.  
     
     
       2. The semiconductor contact structure as claimed in  claim 1 , wherein said conductive material is a region of impurities comprising an upper portion of said substrate. 
     
     
       3. The semiconductor contact structure as claimed in  claim 1 , wherein said conductive material is a conductive pad disposed on the semiconductor substrate. 
     
     
       4. The semiconductor contact structure as claimed in  claim 3 , wherein the conductive pad comprises polysilicon. 
     
     
       5. The semiconductor contact structure as claimed in  claim 1 , wherein the interlayer dielectric layer is of borophosphsilscate glass (BPSG).